Monocrystalline compound semiconductor materials, which are single crystals such as aluminum nitride (also termed “AlN” hereinafter) and gallium nitride (also termed “GaN” hereinafter), to date have been employed in a variety of applications. For example, AlN can be employed in heat sinks, as a material for semiconductor manufacturing devices, and in thin-film pressure sensors, while GaN can be employed in light-emitting devices and electronic devices.
Monocrystalline compound semiconductor materials such as the AlN and GaN single crystal just mentioned are producible by, for example, sublimation deposition. Sublimation is a growth technique whereby source material inside a reaction vessel such as a crucible is put at a high temperature to sublime the material and re-deposit crystal in a lower-temperature area. Sublimation deposition includes techniques based on self-seeding, which do not use starting substrates, and techniques that use monocrystalline heterosubstrates as starting substrates.
In instances where compound semiconductor single crystal is grown using a starting substrate, the necessity of separating the starting substrate and the compound semiconductor single crystal arises. A variety of approaches, such as forming a concave-convex structure in the surface of the starting substrate, in order to be able to carry out separation of the starting substrate and the compound semiconductor single crystal with ease have come about. Herein, Japanese Unexamined Pat. App. Pub. No. 2005-159333 (Patent Document 1) sets forth technology according to which the removal side of a substrate is scribed or laser-beam irradiated to form initiators, whereby the substrate is removed.    Patent Document 1: Japanese Unexamined Pat. App. Pub. No. 2005-159333.